1. Technical Field
The present invention relates to an air cleaner structure in two-stroke engines, and more particularly to an air cleaner structure in a two-stroke engine having an air passage that is connected midway of a scavenging passage communicating a scavenging port with a crank chamber and that supplies leading air from the air cleaner to the scavenging passage, and an air/fuel mixture passage supplying air/fuel mixture created in a carburetor to the crank chamber.
2. Description of the Related Art
A stratified scavenging two-stroke engine includes a scavenging passage communicating a scavenging port provided in a side portion of a cylinder with a crank chamber, an air passage connected midway of the scavenging passage for supplying scavenging air from an air cleaner to the scavenging passage, and an air/fuel mixture passage for supplying air/fuel mixture created in a carburetor to the crank chamber. Prior to supplying the air/fuel mixture from the scavenging port into the combustion chamber, leading air filtered in the air cleaner is introduced through the air passage, scavenging passage, and scavenging port into the combustion chamber for the scavenging effect, to reduce the amount of unburnt air/fuel mixture passing through.
In some stratified scavenging two-stroke engines configured as described above, there may be provided a choke valve for adjusting the amount of air supplied to each of the air passage and the air/fuel mixture passage when the engine is started. In this case, the respective inlets of the air passage and the air/fuel mixture passage may be provided with a separate choke valve, for example. However, providing separate choke valves for the respective inlets of the air passage and the air/fuel mixture passage will make the operating system of the choke valves complex because of the increased number of choke valves, and will increase the size of the entire device associated with the stratified scavenging two-stroke engine.
Japanese Patent No. 4052416, for example, discloses a technique for adjusting the amount of air each supplied to both of the air passage and the air/fuel mixture passage with one choke valve. The patent relates to a two-stroke engine including a scavenging passage communicating a scavenging port provided in a side portion of a cylinder with a crank chamber, an air supply passage connected midway of the scavenging passage for supplying scavenging air from an air cleaner to the scavenging passage, and an air/fuel mixture supply passage for supplying air/fuel mixture created in a carburetor to the crank chamber. The air cleaner includes a first air passage and a second air passage arranged in parallel, the first air passage communicated with the air supply passage and the second air passage connected to an air inlet of the carburetor for supplying air to the carburetor for the generation of the air/fuel mixture. The air cleaner includes a choke valve opening and closing the first air passage and the second air passage. The choke valve includes a rotary valve member opening and closing each of the inlet openings of the first air passage and the second air passage by rotation, and a rotation knob for rotating the valve member. The valve member has a rotation center between the two inlet openings of the first air passage and the second air passage.
Using just one choke valve in this manner makes it possible to avoid the operating system from becoming complex and the entire device from becoming large.
In such a stratified scavenging two-stroke engine, in addition to avoiding the operating system from becoming complex and the entire device from becoming large by using one choke valve as described above, high airtightness is required when the choke valve closes the openings.
The technique disclosed in Japanese Patent No. 4052416 uses a rotary valve member as the choke valve, so that the inlets of two passages are simultaneously opened and closed with one choke valve, whereby the operating system of the choke valve is prevented from becoming complex and the device from becoming large, as well as high airtightness is achieved when the choke valve closes the openings.
However, with the technique disclosed in Japanese Patent No. 4052416, while high airtightness is achieved when the choke valve closes the openings as noted above, there is a problem that processing of the sealing surface for achieving the airtightness is difficult, since the sealing surface is large because of the use of the rotary valve member that has the rotation center positioned between the inlet openings of the two passages.
Accordingly, a choke valve capable on its own, without using a rotary valve member, of opening and closing the inlets of two passages simultaneously and of ensuring high airtightness, is desirable.
A possible solution would be to employ a pivotable choke valve that can open and close the inlets of two passages simultaneously. However, if employed, a simply pivoting choke valve would need a large valve member and a large operating angle range in order to open and close the two passages simultaneously. This will increase the size of the choke valve itself and its work range, which will in turn increase the size of the entire device.